A conventional self-ballasted fluorescent lamp is disclosed, for example, by Japanese Laid-Open Patent Publication No. 2000-21351, which is incorporated by reference in its entirety herein. The conventional lamp typically includes a luminous tube, a holder, a cover, a lighting device, and a globe. The luminous tube may be a bent-type luminous tube mainly comprised of, for example, a plurality of bulbs having a U-like shape and arranged one in front of the other and connected to one another so as to form a single, continuous discharge path. The holder supports an end of the luminous tube. A base is fitted to one end of the cover, and the luminous tube, which is supported by the holder, is provided at the opposite end of the cover. The lighting device is disposed inside the cover. The globe is attached to the other end of the cover and encases the luminous tube. A plurality of bulb insertion holes are formed in the holder, which supports the aforementioned end of the luminous tube. The bulb insertion holes have an inner diameter larger than the outer diameter of each end portion of the bulbs of the luminous tube, and the end portions of the bulbs of the luminous tube are respectively bonded to and thereby affixed in the bulb insertion holes by means of a bonding agen.
Although self-ballasted fluorescent lamps having such a configuration as described above are becoming more compact recently so that their lamp length and maximum outer diameter are similar to those of electric light bulbs for general illumination as defined by JIS Standard, the cover of those conventional self-ballasted fluorescent lamps has a considerably large maximum outer diameter and occupies a proportionally large part of the lamp length. For example, such conventional self-ballasted fluorescent lamps typically have dimensions such that the proportion of the distance by which the cover is exposed from the base to the lamp length excluding the base is not less than 30% and that the maximum outer diameter of the cover ranges from 1.7 to 1.8 times the outer diameter of the base or approximately 80% of the maximum outer diameter of the globe.
The cover of the conventional self-ballasted fluorescent lamp has a considerably large maximum outer diameter and occupies a proportionally large part of the lamp length. Such a large cover not only makes it difficult to bring the appearance of the self-ballasted fluorescent lamp sufficiently close to that of an electric light bulb for general illumination but also makes the light incident upon the cover proportionally larger due to the large outer diameter of the cover, thereby blocking a large proportion of light distribution to the side where the base is provided. As a result, during the time the luminous tube is lit, light distribution characteristics are not sufficiently similar to those of an electric light bulb for general illumination. Although a part of the light incident upon the cover is output as reflected light, some of the light is absorbed by the cover. Furthermore, as the end portions of the bulbs of the luminous tube are respectively bonded and thereby secured in the bulb insertion holes of the holder by means of a bonding agent, the light emitted from the end portions of the bulbs, which are fitted in the holder, shines into the holder and cannot be radiated to the outside. As a result, the optical output of the entire lamp is reduced. These drawbacks of the conventional self-ballasted fluorescent lamp lessens its applicability to a lighting fixture that uses an electric light bulb for general illumination.